?4R00MH106649-03 PI: Avishek Adhikari Modified Project Summary/Abstract Section This proposal will be moved from the mentored phase institution (Stanford University) to the R00 institution (University of California, Los Angeles). No changes have been made to the experimental plans. The current proposal is specific to the R00 phase. Avoidance of potential threats is highly adaptive, and decreases exposure to risks. However, excessive anxiety and fear leads to anxiety disorders, which impact many aspects of life, from the interpersonal to professional spheres. Although each anxiety disorder has different symptoms, they all share a core feature: mal-adaptive expression of high levels anxiety. Here, we will study how the brain suppresses anxiety. Prior studies showed the amygdala is largely responsible for generating high anxiety and fear, while the ventral medial prefrontal cortex (vmPFC) decreases these behaviors, possibly by inhibiting amygdala output. Indeed, in humans higher vmPFC activation correlates with lower amygdala activation and decreased anxiety. These data suggest the vmPFC-amygdala pathway may decrease anxiety and fear, but they rely on correlative measures, and can't directly test this hypothesis. I used optogenetics to directly test if the vmPFC-amygdala projection suppresses anxiety and fear. Activation of the vmPFCamygdala pathway robustly inhibits innate anxiety and learned fear, while inhibition of this pathway increases anxiety. Intriguingly, these behavioral effects were mediated by a poorly studied region of the amygdala called the basomedial amygdala (BMA), as direct activation of the BMA also decreases anxiety. Now, I will map neural activity in the vmPFC-BMA circuit and dissect how activation of this circuit decreases anxiety. We first showed how vmPFC activity affects the BMA in vitro (Aim 1), uncovering the microcircuit-level dynamics underlying our behavioral findings. Next, to map the activity of the vmPFC-BMA projection, I will monitor calcium transients in the vmPFC terminals in the BMA during exploration of control and anxiogenic environments (Aim 2), revealing how activity of this projection differs in animals with high and low anxiety. In Aim 3, I will characterize activity of the BMA and of its output projections during anxiety and fear. The insights resulting from this project will guide future studies on anxiety.